1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for performing the printing by discharging inks to a recording objective medium, and an ink cartridge set to be used therefor.
2. Description of the Related Art
An ink-jet printer is known, which performs the printing by discharging an ink from nozzles of an ink-jet head to recording paper. In general, such an ink-jet printer is provided with a detachable ink cartridge for supplying the ink to the ink-jet head. When the ink-jet head is driven to perform the discharge operation in a state in which the ink is empty in the ink cartridge, then the printing is not only performed, but the air sometimes makes invasion from the ink cartridge into the ink-jet head. The ink-jet head, into which the air has made invasion, cannot be used in some cases. Therefore, it is necessary to detect the amount of the ink stored in the ink cartridge. A method for detecting the amount of the ink is conceived, in which the amount of the ink is detected by estimating and accumulating the amounts of the ink used every time when the printing is performed. However, any error tends to arise in such calculation. Therefore, it is necessary to stop the use of the ink cartridge with a sufficient margin. As a result, the ink is wasted. Accordingly, the following technique has been suggested (see, for example, Japanese Patent Application Laid-open No. 9-001819, FIG. 7). That is, a float, which has a specific gravity smaller than that of the ink, is arranged on the ink stored in the ink cartridge. The height of the float floating on the ink is detected from the outside by using an optical sensor to detect the amount of the ink contained in the ink cartridge thereby.
A dye ink, which has light transmittance or transparency, is generally employed for the ink to be used for the ink-jet printer. However, a problem has arisen such that the contour tends to be fuzzed especially when letters are printed, because the ink is blurred on the recording paper. Therefore, it is demanded that the black ink, which is frequently used in the recording of letters, is a pigment ink which has the nontransparency in order to perform the printing of higher quality. However, when it is intended to detect the ink amount by the technique as described above for the ink cartridge which uses the pigment ink, the following problem arises because both of the ink and the float have the nontransparency. That is, it is impossible to detect only the float with the optical sensor, and it is impossible to detect the correct ink amount. Accordingly, it is conceived that the ink itself is detected directly by using the optical sensor for only the ink cartridge which uses the ink having the nontransparency. A light-transmissive type sensor, in which the cost is relatively cheap, is generally used as the optical sensor to be employed for the detection. However, when the detection is performed more accurately, or when a sensor, which is relatively unsatisfactory in accuracy, is used in order to further decrease the cost, it is conceived that the thickness of a portion for accommodating the ink as a detection objective is partially thinned in order to shorten the distance between a light-emitting section and a light-receiving section of the sensor. However, as for the ink disposed at the portion which is partially thinned, the ink is adhered to the wall surface by the surface tension, and the ink liquid surface is raised. Therefore, a problem arises such that a liquid surface, which is higher than the actual ink liquid surface, is detected, and it is impossible to correctly detect the predetermined ink amount.